In recent years, a sealing-and-pump-up device, which is used to repair a puncture when it occurs in an air-inflated tire (hereinafter, simply referred to as “tire”) by injecting a liquid sealant into the inner side of the tire and elevating the inner pressure of the tire up to a specified pressure without replacing the tire and wheel, has become widely used. Examples of the sealant used in the sealing and pump-up device of this kind include one produced by agitating and mixing a mixture of a rubber latex, a resin emulsion, and an anti-freezing agent consisting of propylene glycol. In general, in the production process of such sealant, the rubber latex and an adhesive agent are mixed so as to prepare a mixed liquid, and then the anti-freezing agent is incorporated into the resultant mixed liquid so as to prepare a stock liquid of sealant. However, propylene glycol rapidly absorbs water from the rubber latex that is present nearby and contacts to the propylene glycol when the propylene glycol is incorporated in the mixed liquid, because propylene glycol used as the anti-freezing agent is an extremely highly miscibile to water. Due to this, the concentration of rubber particles contained in the latex that is present nearby the propylene glycol becomes extremely high to have the rubber particles aggregate and form aggregates, and thus, a phenomenon that a part or whole of the sealant solidifies (gells) by employing the aggregates as cores of the solidification tends to occur.
As a method for producing a sealant which aims preventing the generation of the aggregates, for example, a method described in Patent Document 1 has been known. The method for producing the sealant described in Patent Document 1 includes a step of incorporation and agitation of an anti-freezing agent in which the anti-freezing agent is incorporated in a mixed liquid of a rubber latex and an adhesive agent that is accommodated in a cylindrical vessel and agitate the mixture. In the incorporation and agitation step, the anti-freezing agent is incorporated into the surface of the mixed liquid through plural inlets at a relatively slow rate of 0.01 to 1.0 liter/min per one inlet, while the mixed liquid is agitated with agitation vanes at a relatively fast vane-tip speed of 1.0 to 10.0 m/sec.
According to the method for producing the sealant described in Patent Document 1, propylene glycol is incorporated little by little at a slow rate into the surface of the mixed liquid while the mixed liquid of the rubber latex and adhesive agent is agitated at the speed described above, so that propylene glycol can be prevented from rapidly absorbing water from its surrounding and that the concentration of the latex particles can be prevented from being locally increased. As a result, one may expect to obtain an effect that the latex aggregates that are formed by aggregation of plural latex particles are effectively prevented from being formed in the stock liquid of the sealant.
Further, Patent Document 1 describes that the agitation is preferably continued for a certain length of time (5 minutes or more, for example) after the incorporation of the anti-freezing agent (ethylene glycol) is completed. This is because aggregation and growth of fine latex aggregates that are formed in the stock liquid of sealant during the agitation can be promoted by continuing the agitation for a certain length of time. This enables easier removal by filtration of the latex aggregates from the stock liquid of sealant than if the latex aggregates are left in a fine size in the stock liquid of sealant.
The present inventors found that, when a certain amount or more of the latex aggregates remain in the product sealant because of incomplete removal of the latex aggregates from the stock liquid of sealant, there may occur a phenomenon in which the latex aggregates serve as cores to promote the gelling of the sealant. There is a concern that the ability of the sealant to seal puncture holes could deteriorate over time due to this phenomenon. Further, there is a concern that over a long period of time the whole of the sealant will become gelled and cannot be injected into a tire.    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-342551